INTRODUCTION TO ENVIRONMENTAL ENGINEERING Final Exam

							ENGS-37                                           Fall 2009
           INTRODUCTION TO ENVIRONMENTAL ENGINEERING

                                      Final Exam


Assigned: 10:00 am Saturday 5 December 2009
Due:      5:00 pm Wednesday 9 December 2009


Note: Please type your answers and start every problem on a new page.
Rule of engagement: No communications among students. Questions may only be
directed to the instructor and TAs.




                                      www.bbc.co.uk

1. (10 points) A 50-50 mixture on a molar basis of methyl mercaptan (CH3SH) and
methanol (CH3OH) is being destroyed by incineration on a continuous basis. The rate of
disposal is 450 kg/hour. The exhaust out of the smokestack is entirely gaseous and enters
the atmosphere at a temperature of 115oC.
    (a) (2 points) What are the combustion reactions?
    (b) (3 points) What is the minimum airflow (in m3/s at 15oC and atmospheric
       pressure) necessary to guarantee complete combustion of both substances?
    (c) (2 points) What is the chemical composition of the fumes on a molar basis?
       [Hint: Do not forget the components of air that do not participate in the
       combustion.]
    (d) (3 points) What is the volumetric flowrate (in m3/s) of the fumes?
                                       farmenergy.org

2. (10 points) An anaerobic digester is commonly used for processing the non-recycled
portion of the sludge in wastewater treatment. This generates carbon dioxide and
methane, and because methane is a greenhouse gas and can be used as a fuel, the
emanations from the digester are collected in a large tank. The temperature is slightly
elevated because of the biological activity, and the pressure is allowed to build up until a
maximum pressure is reached. Once the maximum pressure is reached, the gas mixture is
drawn out and used.
    Consider the specific situation. A 1000 m3 tank holds a gas mixture that is 65%
methane (CH4) and 35% carbon dioxide (CO2) on a volume basis at a pressure of 3 atm
and at a temperature of 35oC.
    (a) (4 points) What mass of each gas is contained in this tank?
    (b) (3 points) How much more mass of methane could be held in the tank if the
        temperature were decreased to 25oC and the pressure remained the same?
    (c) (3 points) If the rate of gas production is 400 kg/day at 35oC, what is the average
        residence time of a gas molecule in the tank?
3. (10 points) In discussions of renewable energy, there is always mention of some
primary, renewable sources of energy, such as the sun, then mention of conversion
technologies, such as photovoltaic cells, to arrive at a derivative form of energy, such as
electricity. Sometimes, the chain goes on, such as electricity passing through an
electrical motor to generate mechanical motion.
    List several other energy chains, of the types:

Renewable source of energy ––(conversion technology)→ Intermediate form of energy
  Intermediate form of energy ––(conversion technology)→ Useful form of energy

Grading rule: 1 point for every correct energy type and 1 for every correct conversion
technology, but minus 1 point for every incorrect energy type (such as non-renewable
form of energy or not ultimately derived from a renewable source), incorrect conversion
technology, and incorrect association.




4. (10 points) There are many variations of the so-called IPAT equation. One of them,
for the automobile, reads as follows:

                   Pollution units of fuel miles trips
       Impact =                ×          ×      ×     × number of cars
                  unit of fuel   mile       trip   car

(a) (2 points) In this equation, separate the technological factors, upon which engineers
    can improve, from the behavioral factors.
(b) (2 points) Write a similar equation for buildings, with at least 4 factors.
(c) (6 points) Identify two technological factors in the equation you just wrote and
    briefly discuss how engineers can design better buildings to lower these two factors.
5. (10 points) The performance of photovoltaic cells is projected to increase
significantly in the near future, and it may be time to rethink the possibility of a solar car,
that is, an electric car fitted with solar arrays on its body. Consider then a small vehicle
(gross weight of 700 kg plus one 70-kg driver, not counting the batteries) that would be
fitted with a 30 kW (40.2 hp) electric motor and the body of which would be covered
with 35% efficient photovoltaic cells. Assume that it would be used in sunny southern
California where one can count on a solar radiation of 1124 W/m2 during daytime.




                               http://www.f9solar.com/site/?q=node/12


(a) (2 points) How much surface area of the vehicle (in m2) would have to be covered by
    photovoltaic cells to provide the 30 kW on an as-you-go basis?
(b) (2 points) Given that the preceding answer exceeds the surface available on the
    vehicle body, some battery storage is required. How many kWh of electricity needs
    to be stored on board the vehicle if the solar radiation can be captured during seven
    hours of the day and the car is driven only twice a day, 20 minutes to go to work in
    the morning and 30 minutes to go home and run an errand in the late afternoon? How
    much photovoltaic cell area is now required? Is such area available on the vehicle’s
    exterior?
(c) (2 points) For lithium-ion batteries that can hold 175 Wh/kg and with a 100% margin
    (i.e. doubling the storage capacity in anticipation of cloudy days and occasional
    heavy traffic), how much battery (in kg) is required?
(d) (3 points) There is a problem, however, with the previous calculation. The weight of
    the battery pack is significant compared to the rest of the weight of the vehicle, and
    added weight to be carried around demands added power. Assuming that the power
    required of the vehicle is proportional to its total weight (700 kg + driver + batteries),
    at the rate of 37 Watts needed per kg, determine the corrected vehicle characteristics:
    weight of battery pack (in kg), power needed (in kW) and surface area of photovoltaic
    cells (in m2).
(e) (1 point) Is a solar car feasible in the near future? Give at least three arguments in
    support of your conclusion.